Typical examples of an infrared signal processing circuit are: remote controllers of home electric appliances and peripheral devices of personal computers, each of which performs data communication in compliance with IrDA (Infrared Data Association) standard. Such an infrared remote control receiver receives ASK (Amplitude Shift Keying) signals (remote controller transmission signals) modulated by a predetermined carrier of, for example, approximately 30 kHz to 60 kHz.
Here, light from a home-use inverter fluorescent light also contains carrier components of 30 kHz to 60 kHz. For this reason, an infrared remote control receiver, when used around a fluorescent light, may malfunction by detecting noise stemming from the fluorescent light. In worst situation, the infrared remote control receiver may not be able to accurately receive signals transmitted from the remote control.
To solve this problem, a data transferring system disclosed in Patent citation 1 (Published Japanese Translations of PCT International Publication for Patent Applications: 502147/2001 (Tokuhyou 2001-502147; Published on Feb. 13, 2001)) is provided with a certain period range T check. The system judges whether a received signal is an infrared signal or noise, according to whether or not a halt period Td occurred within the period range T check. If the signal received is judged as to be noise, an amplifier is controlled. However, an infrared signal can vary depending on makers, and there are more than ten different kinds of infrared signals: e.g., NEC codes, Sony codes, RCMM codes, etc. Thus, some infrared signals are not adaptable to the halt period Td of the data transferring system, and the system is not able to receive those inadaptable infrared signals.
Furthermore, in a receiver circuit disclosed in Patent citation 2 (Published Japanese Translations of PCT International Publication for Patent Applications: 506375/2004 (Tokuhyou 2004-506375; published on Feb. 26, 2004)), an output signal from a bandpass filter is demodulated, and the demodulated signal is used as a trigger for controlling an amplifying circuit and the bandpass filter. However, this receiver circuit has the following problem. Namely, when noise from fluorescent light having a high illuminance is incident on the receiver circuit, the output signal of the bandpass filter is saturated by the noise. This causes the demodulated signal to be constantly in the L level. Due to this, the demodulated signal does not function as the trigger, and as the result, the amplifying circuit and bandpass filter are not controlled.